To store and transport flowable materials such as grain, chemicals, fertilizers and minerals, intermediate or semi bulk shipping containers have been developed. These containers are often square or rectangular in design and constructed of a rigid material, such as corrugated paper board. The containers hold approximately 1,000 to 3,000 lbs. or more of bulk material and because of their economical design, are readily stacked for high density storage or transportation.
As a result of the inherent properties of flowable or bulk material, bulk material exerts a lateral force upon the side wall panels of bulk containers. The box like shape of the containers do not permit the uniform distribution of the lateral forces. Hence, bulging of the container may result. Bulging is an undesired effect as it distorts the containers causing a loss of storage space when the containers' are stacked together. In the extreme, bulging can cause rupture of the containers and a spilling of the containers' contents. This is especially undesired when the contents are chemical in composition.
To compensate for the lateral forces exerted by the flowable materials, square or rectangular (i.e, box) rigid bulk containers are made of durable material (e.g., reinforced corrugated paper board) which are capable of withstanding the lateral forces. Such durable material is more expensive than standard packaging material. Moreover, the manufacture of the rigid containers is more complex as a result of construction techniques designed to add strength to the containers to compensate for the lateral forces.
U.S. Pat. Nos. 3,543,991 and 3,715,072 each describe a rectangular shaped rigid bulk container. Three individual cells are formed from corrugated paper board and may contain both a bottom and top closure flaps. The cells are placed in side by side relation and are interconnected via attachment of respective adjacent panels. Reinforcing side panels may be positioned to overlie the external side panel of the first and third cells. A bottom tray and top tray may be placed over the respective top and bottom ends of the container. U.S. Pat. No. 3,715,072 further describes the adhesion of reinforcing sheets between adjacent side walls of individual cells to enhance bulge resistance and to distribute pressure uniformly along the adjacent side walls of the cells.
The rectangular shaped rigid intermediate bulk containers of the type described in U.S. Pat. Nos. 3,543,991 and 3,715,072 are more expensive as a result of manufacturing costs due to the composition of the containers necessitated by the square or rectangular design (which does not uniformly distribute the lateral forces exerted by the flowable material) and the overall complexity of the configured containers. Moreover, these containers are still susceptible to bulging, despite their construction.
As an alternative, hybrid bulk containers have been developed which combine rigid square or rectangular containers, and circular flexible bulk containers. U.S. Pat. Nos. 4,834,255; 4,901,885; 4,927,037; 5,052,579; 5,071,025; 5,282,544; 5,289,937; and 5,407,090 each describe a bulk container having an outer rigid container of rectangular design and an inner circular flexible container. The inner circular flexible container functions to deflect the lateral forces exerted by the flowable materials (which are chiefly contained within the flexible container) and relieve the bulge pressure, which in a standard rigid container would have been exerted against the container's side walls. Again, this configuration suffers from the disadvantages of increased costs and complexity.
It is therefore an object of the present, invention to overcome the draw backs associated with bulging of rigid rectangular or square bulk containers under load. This object is achieved through the use of vertical side beams positioned about the side wall panels of the bulk container.